Aircraft antenna with impedance matching device



May 13, 1958 w. P. LEAR, sR.. ETAL ,33

AIRCRAFT ANTENNA WITH IMPEDANCE MATCHING DEVICE Filed March 7, 1955 INVENTORs: Wllllam Powell Lear, 5r. Clyde KIA/Z7710. 7 1

United States Patent AIRCRAFT ANTENNA WITH IMPEDANCE MATCHING DEVICE William Powell Lear, Sr., Prevorzier, Mies, Switzerland, and Clyde J. Norton, Canogo Park, Calih, assignors to Lear, Incorporated, Grand Rapids, Mich.

Application March 7, 1955, Serial No. 492,658

8 Claims. (Cl. 343-860) This invention relates to antennae for transmitting and receiving electromagnetically radiated energy. In particular, it has reference to,an antenna construction for installation on aircraft for ground plane reception and transmission with the feed point tapped up from the grounded end for a coaxial feed line, and preferably provided with an impedance-matching stub.

One of the principal objects of the invention resides in an antenna as aforesaid provided with a co-axial impedance matching section mounted within a hollow mast antenna portion.

Another important object lies in providing a novel construction of hollow antenna mast including a plurality of sections carried 'end-to-end by means of electrically-insulating joints having great rigidity forming an integral part of the mechanical structure.

A further object is to provide an antenna as aforesaid in which various electrical joints.,may be made up intermediate the confronting, spaced-apart ends of the mast sections and the sections thereafter united with an electrically-insulating joint which also protects the joints therewithin.

Another object is to provide an antenna assembly which may be mounted by one end directly on the skin of the aircraft and wherein both the upper and lower portions of the antenna may be at ground potential.

Other objects will become apparent from the following description, which, taken with the accompanying drawing, discloses a preferred form which the invention may assume in practice.

In this drawing:

. Fig. l is a side elevation of an antenna in accordance with the invention, mounted on an aircraft;

Fig. 2 is an enlarged elevational view, partly in cross section;

Fig. 3 is a top plan view of the antenna;

Fig. 4 shows a cross section on the line 4-4 of Fig. 2;

and

Fig. 5 is a cross section on the line 5--5 of Fig. 2.

Referring to the drawing, there is shown an antenna comprising a lower mast section and an upper mast section 11, together being suitably formed to provide an esthetic, swept-back configuration having appropriate streamlining and positioning for aerodynamic considerations.

The sections 10 and 11 may be of any suitable metal, e. g. aluminum and cast or otherwise formed to define respective chambers 14 and 15, although the upper section may be solid. The section 10 has a flange or base 16 including holes 17 for the reception of bolts whereby the antenna may be secured to the metallic skin of the airplane for electrical, i. e. ground connection thereto. Section 10 is also provided with a thickened wall portion 21 for the reception of screws 22 serving to attach a metallic or other conducting plate 24 conformed peripherally to the extremity, which latter is reduced cross-sectionally around its periphery to define a hub 27 for a purpose to appear.

The upper section 11 is similar to the section 10 and includes a plate 29-similar to the plate 24 and a reduced end defining a hub 31.

Connection to the center point of the antenna is via a suitable transmission line, e. g. a coaxial conductor 41, the outer member or braid 42 whereofis soldered to the connector housing 43 and the central member whereof is connected to a rigid terminal pin 44, both of which are of a common type for connection to a co-axial lead extending from the transmitter and/ or receiver of the craft. Part 43 is grounded by screws 46 secured to the base 16.

The grounded braid 42 is soldered at 48 to the margin of an aperture 49in the plate 24 in order to lend rigidity thereto and the center conductor 50 'is carried upwardly and soldered to a struck-out lug 51 of the plate 29 for electrical connection to the upper antenna section 11.

In order to obtain an adjustable or predeterminable impedance match, there is provided a stub section comprising two parallel conductors preferably in the form of a length of co-axial cable 55 having an inner con ductor 56 soldered to the conductor 50, the outer conductor or braid 57 thereof soldered at its upper or proximal end to the margin of a second aperture 58 in the plate 24 for grounding thereof (Fig. 4), and covered by an insulating sleeve. At the lower or distal end of the stub 55 the braid 57 and the lead 56 are soldered together, to close the stub, and the same is securely lashed at 61 to some convenient fixed part, e. g. the cable 41,

From the foregoing, it will have been apparent that, pending securement ofthe several electrical connections to and intermediate the plates 24 and 29, the body sections 10 and 11 are maintained in properly spaced relation by means of a suitable jig. Subsequent to the assembly steps heretofore outlined, wrapping 63 is applied over the reduced end sections 27 and 31 by winding a suitable insulating fabric or paper thereover, e. g. glass cloth impregnated with a suitable thermoplastic dielectric material. Such wrapping is continued to the point where flush relation with the exterior of the sections 10 and 11 is achieved, whereafter integration of the several turns of cloth to each other and to the contiguous metal surfaces, may be realized by appropriate curing action, e. g. heat. The net result is a rigid antenna assembly of smooth streamline configuration particularly adapted to aircraft use.

The gap intermediate the plates 24 and 29 corresponds approximately to the center tap of the antenna and its longitudinal position determines the electrical impedance thereof. As the gap is moved upwardly (all other dimensions being unchanged), the impedance presented to the feed 41 is increased.

Assuming a design providing a A wave length ground plane antenna, the gap location can be selected to provide an upper antenna section of approximately 4; wave length, and the matching stub is then A wave length.

By virtue of the matching stub 55, the upper portion of the antenna is at ground potential for D. C., i. e. voltages induced by lightning, since the braid of the stub is at ground potential and is shorted to its center conductor.

The effect of the matching stub is to increase the band width of the antenna. In the absence of the stub, the antenna will, at its resonant frequency, present a resistive load to the transmission line. Below resonant frequency, the antenna will prevent a load which appears as a resistance-capacitance parallel combination. Above resonant frequency, the load will appear as a resistanceinduetance parallel combination. The shorted stub provides a reactance characteristic which varies inversely to that of antenna. Accordingly, the net result is a more nearly constant impedance over the required range of frequency.

An antenna in accordance with the invention designed Patented May 13, 1958 3 for operation over the wide range from 118 to 140 mc. and having an impedance of 50 ohms, is characterized by a voltage standing wave ratio of less than 2:1, thus permitting the antenna to radiate power over the entire range with almost constant efiicicncy.

While we have shown particular embodiments of our invention, it will be understood, of course, that we do not wish to be limited thereto, since many modifications may be made, and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention We claim:

1. A broad band antenna construction comprising an elongated, hollow, lower section having means for supporting the antenna, an elongated Up er section aligned with said lower section and spaced therefrom, a transmission line passing into said space and connected to the upper section, an impedance-matching stub connected to said line at a position in said space, said sections each having a reduced end portion adjacent said space, and an electrically insulating, rigid sleeve fitted over said portions, the exterior surfaces of said sleeve and sections being in flush relation.

2. A broad band antenna construction adapted to be supported in upstanding position on an exposed aircraft surface comprising an elongated, hollow, lower section including a flange at the lower end for securement to the surface, and a wall closing the upper end thereof, an upper section in alignment with and spaced from said lower section, a two-conductor transmission line passing through said lower section and into the space intermediate said sections, one conductor being connected to said upper section, an impedance matching stub connected to said transmission line in the space intermediate said sections, the other conductor of said line being adapted for grounding and electrically connected to said wall, and an electrically insulating sleeve embracing said sections and enclosing said space, said sleeve being secured to said sections by means of cementitious material.

3. A broad band antenna construction adapted to be supported in upstanding position on an exposed aircraft surface comprising an elongated, hollow, lower section including a flange at the lower end for securement to the surface and a wall closing the upper end thereof, an upper section in alignment with and spaced from said lower section, a co-axial transmission line including a center conductor passing through said lower section and into the space intermediate said sections and connected to said upper section, the outer conductor being grounded, an impedance matching stub connected to said transmission line in the space intermediate said sections, said line having a cylindrical shield adapted for grounding and electrically connected to said wall, each said section being cross-sectionally reduced for-a distance on each side of said space, and an electrically insulating sleeve enclosing said space rigidly bonded to said sections over said reduced ends and flush with the exterior surface of said sections.

4. A broad band antenna construction comprising a first, elongated, tubular section having means for securing the antenna to a support, a second elongated, tubular section in alignment with and confronting said first section and spaced therefrom to define a conductor-manipulating and connecting space, a plate secured to the end of each section bordering said space, a co-axial transmission line passed through said first section, the plate of said first section having an aperture for passage of the central conductor of the line and the shield whereof is connected to the margin of said aperture, the end of the conductor traversing said space and being connected to the other plate, an electrically-insulating sleeve enclosing said space for maintaining rigidly the aligned, spaced relation of the sections, said sections having reduced portions at the confronting ends to receive the respective ends of the sleeve to provide an unbroken surface aspect from one outer end i of the assembled sections and sleeve to the other.

5. The combination in accordance with claim 4 further characterized by a co-axial impedance matching stub, said plate of the first section having a second aperture for passage of the central conductor of said stub, the shield whereof is connected to the margin of the second aperture, said two central conductors being joined in said space.

6. The combination in accordance with claim 6 wherein the stub is positioned within the first section and the conductor and shield whereof are connected together at the end opposite the end connected to the transmission line.

7. An antenna comprising a first electrically conducting portion including a part for connection to an electrical ground, a second electrically conducting portion spaced apart from said first portion and aligned therewith, a twoconductor transmission line, one conductor of which is electrically connected to said second portion, and the other conductor of which is electrically connected to said first portion, an impedance matching stub comprising two parallel conductors, one conductor thereof being connected to the junction of the said other conductor to the said first portion, the distal ends of the stub being joined and the other conductor of the stub being connected to ground at its proximal end.

8. Au antenna comprising a first electrically conducting portion including a part for connection to electrical ground, a second electrically-conducting portion spaced apart from said first portion and aligned therewith, a coaxial transmission line, the inner conductor of which is electrically connected to said second portion and the outer conductor of which is connected to said first portion and to ground, a co-axial impedance matching stub, the inner conductor whereof is connected to the junctions of said transmission line inner conductor and second portion, the inner and outer conductors of the stub being joined at their distal end, and the outer conductor of the stub being connected by its proximal end to said first portion.

References Cited in the file of this patent UNITED STATES PATENTS 

